Process for the production of activated coke for simultaneous desulfurization and denitrification

ABSTRACT

Disclosed is a process for the production of high-strength activated coke for desulfurization and denitrification. The process comprises forming a mixture of plural coals of different caking properties and a binder, said mixture containing said coal of higher caking property in an amount of 10-50 wt. %, subjecting the thus-formed mixture to oxidization treatment in an atmosphere having an oxygen concentration of 1-18 vol. % and a temperature of 50°-250° C., subjecting the thus-treated mixture to carbonization treatment under conditions of an oxygen concentration not higher than 8 vol. %, a heating efficiency of 10°-50° C./min and a final temperature 600°-900° C., and then subjecting again the thus-carbonized mixture to oxidation treatment at an oxygen concentration of 3-18 vol. % and a temperature of 200°-600° C. By treating the resultant high-strength activated coke for desulfurization and denitrification further with concentrated sulfuric acid, a coke which is inherently equipped with high denitrification activity can be obtained.

This application is a continuation of application Ser. No. 08/481,350,filed Jul. 6, 1995, now abandoned.

TECHNICAL FIELD

This invention relates to a technique on an activated coke forsimultaneous desulfurization and denitrification, and especially to atechnique for producing a useful activated coke for concurrentdesulfurization and denitrification, said coke being suitable for use asa denitrification catalyst in a dry desulfurization and denitrificationprocess.

BACKGROUND ART

For the removal of sulfur oxides and nitrogen oxides which are containedin flue gas, many wet and dry, desulfurization and denitrificationprocesses have been proposed and practiced. Among these desulfurizationand denitrification processes, the dry processes have been attractingincreasing interests in recent years owing to the merits that they donot require complex waste water treatment facilities, whose maintenanceand control are difficult, and they do not need a large area for plantinstallation.

In these dry desulfurization and denitrification processes, variousadsorbents and catalysts are employed. Among these, carbonaceousmaterials obtained by granulating or otherwise forming activated carbonas a principal raw material are used especially widely by usingabilities for desulfurization and denitrification of the activatedcarbon.

As plants for practicing dry desulfurization and denitrification, thoseof the moving bed system have been predominantly adopted. In theseplants, a carbonaceous adsorbent is generally recycled and reused.Conventional granulated or otherwise formed carbonaceous adsorbents arehowever accompanied by such practical problems to be resolved that theyare low in compressive strength, abrasiveness, shatter strength and thelike and are hence worn out or otherwise lost considerably whenrepeatedly used through adsorption and regeneration.

There is known, for example, a production process in which a coal, whosecaking property has been eliminated by subjecting it beforehand tocarbonization or oxidation treatment in a temperature range of 250°-600°C., is added and mixed with another coal having caking property and abinder to adjust the caking property, the resultant mixture is formed,the thus-formed material is carbonized at a temperature of 800°-900° C.(heating efficiency: 10° C./min or less) and an oxygen concentration of0 vol. %, and the thus-carbonized formed material is then activated withsteam at a temperature of 800°-900° C. to obtain an activated coke. Bytreating the coal in advance and hence eliminating its caking property,this process achieves prevention of deformation, breakage or the like ofthe formed material due to its expansion or the like in thecarbonization step and also formation of uniform pores upon conversioninto the activated coke. The activated coke obtained as described above,however, has contributed extremely little to an improvement in thedenitrification efficiency despite the specific surface area has beenincreased by conducting the activation treatment.

Further, research and development work are under way on adsorptivecarbonaceous materials to further enhance their desulfurization anddenitrification performance. This approach include, for example, toincrease surface functional groups on a carbonaceous material. Thisapproach may be able to improve abilities for desulfurization anddenitrification but, due to a substantial reduction in strength by theactivating treatment itself, it can obtain only a low-strengthcarbonaceous adsorbent. On the other hand, carbonaceous adsorbentsdeveloped with a primary object focused at their strength areaccompanied by the problem that their initial desulfurization anddenitrification performance is not sufficient.

Also developed are those obtained by having a metal or the like carriedon an activated coke so that their performance for nitrogen oxides havebeen enhanced. To employ them in a dry desulfurization anddenitrification process of the moving bed system, however, theirpoisoning by sulfur oxides, worn-out or loss, reduction in performanceafter regeneration, and the like cannot be ignored.

In addition, techniques have also been studied and developed forobtaining an activated coke by adding a caking coal or a non-caking coaland also a binder. These techniques include, for example, processes inwhich a caking coal or a non-caking coal is crushed, formed withoutaddition of a binder, oxidized and then carbonized (dry-distilled) andoptionally, the product so obtained is activated further (JapanesePatent Laid-Open No. 69312/1990, Japanese Patent Laid-Open No.55788/1990, etc.) as well as processes in which a mixture of a cakingcoal, a non-caking coal and a binder is formed, followed by oxidationand activation (Japanese Patent Laid-Open No. 129813/1988, etc.). Thereare also processes for the production of a desulfurizing carbonmaterial, in which physical properties of a mixture of a caking coal, anon-caking coal and a binder are adjusted to have specific values(Japanese Patent Publication No. 17761/1988, etc.).

Despite various techniques have been studied to date as described above,even those obtained by these processes have low denitrificationperformance so that, even if they are activated cokes excellent inmechanical strength and desulfurization performance, they cannot stillmeet practical performance requirements for use in simultaneousdesulfurization and denitrification.

From such a technical background, there is a long standing demand for anactivated coke having high abilities for desulfurization anddenitrification and, moreover, such high strength as being capable ofwithstanding recycled use in a dry desulfurization and denitrificationprocess of the moving bed system.

DISCLOSURE OF THE INVENTION

With a view toward resolving the above-described technical problems, thepresent invention has as an object thereof the provision of a processfor producing an activated coke which has high abilities fordesulfurization and denitrification and, moreover, such high strength asbeing capable of withstanding recycled use in a dry desulfurization anddenitrification process of the moving bed system.

As a result of an extensive investigation, the present inventors havefound that an activated coke formed using a coal as a primary rawmaterial, specifically, an activated coke having high abilities fordesulfurization and denitrification and also sufficiently high strengthcan be obtained by blending coals as raw materials at a particular ratiofrom the standpoint of caking property, forming the coal blend and thentreating the thus-formed coal blend under specific conditions, leadingto the completion of the present invention.

The present invention therefore provides a process for the production ofan activated coke for desulfurization and denitrification from coal as aprincipal raw material, which comprises adding a binder to a coal blend,said coal blend having been obtained by blending at least one coal ofdifferent caking property, the proportion of said coal of greater cakingproperty being 10-50 wt. %; forming the resultant mixture; oxidizing thethus-formed material in an atmosphere having an oxygen concentration of1-18 vol. % and a temperature of 50°-250° C.; carbonizing thethus-oxidized mixture at an oxygen concentration not higher than 8 vol.% and a heating efficiency of 10°-50° C./min to a final temperature600°-900° C.; and then oxidizing the thus-carbonized formed material atan oxygen concentration of 3-18 vol. % and a temperature of 200°-600° C.

Further, two or more coals having high caking property can be used inthe present invention. In this case, it is necessary to limit theproportion of the coal, which has the highest caking property, at 10-50wt. %.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, at least two coals of different cakingproperties, which include at least one caking coal, are used asprincipal raw materials, and the proportion of the caking coal whereonly one caking coal is used or the proportion of the caking coal havingthe highest caking property where two or more caking coals are employedis set at 10-50 wt. %. Namely, upon blending coals, at least two coalsof different caking properties are blended. Here, at least one cakingcoke is blended. Accordingly, the blend of two coals of different cakingproperties is either a combination of a caking coal and a non-cakingcoal or a combination of caking coals. The proportion of the caking coalin the former combination or the proportion of the coal having highercaking property in the latter combination is set at 10-50 wt. %.

It is of course possible to use plural, e.g., three or four coals ofdifferent caking properties. In this case, the proportion of the coalhaving the highest caking property is set at 10-50 wt. %.

Where the coal blend contains only one caking coal and its proportion islower than 10 wt. % or where the coal blend contains two or more cakingcoals and the proportion of the caking coal having the highest cakingproperty is lower than 10 wt. %, neither coal blends cannot provide afinal product of high strength so that the object of the presentinvention cannot be attained. If their proportions exceed 50 wt. %, onthe other hand, the formed materials are each caused to swellextraordinarily or fuse together during the carbonization step so thatgood products cannot be obtained.

Use of such a composition makes it possible to allow the coals toundergo oxidation to different extents in the subsequent oxidation stepso that high strength can be retained after the carbonization.

The coals may be crushed in the form of a blend. As an alternative,coals which have already been crushed to a predetermined particle sizemay be blended. As the particle size of the coals, the particle diametermay preferably be 0.5 mm or smaller in view of formability, readiness inoxidation in the oxidization step, and the like.

Incidentally, coals are classified into brown coal, subbituminous coal,bituminous coal, anthracite, etc. in the increasing order of the degreeof metamorphism. A coal having high caking property is primarilyproduced as bituminous coal in general. In each class, coals can also beclassified according to caking property into non-caking coals and cakingcoals. The coal of high caking property, which is usable in the presentinvention, means the property determined based on a mutual relationshipbetween coals to be used but does not mean the property determinedindependently with respect to a single coal.

The coals, which are to be used as raw materials in the above-describedforming, are added and mixed with a binder. The resultant mixture iskneaded and formed into a formed coal. As the binder, one havingstickiness, for example, tar, pitch, a resin, pulp mill waste water orthe like can be used. The mass so mixed and kneaded is formed using, forexample, a briquetting machine, a pelletizer, an extruder or the like,thereby obtaining a formed material having a particle diameter ofapproximately 5-20 mm.

The formed material so obtained is subjected to oxidation treatment for10-180 minutes under conditions of an atmosphere having an oxygenconcentration of 1-18 vol. % and a temperature of 50°-250° C. Dependingon the composition of the coals, these conditions can be suitably setwithin the respective ranges. Where coals to be mixed are, for example,both caking coals and the proportion of the caking coal having highercaking property is above 20%, it may be sufficient to conduct oxidationtreatment for 1 hour or so provided that the oxygen concentration is 12vol. %. Upon conducting the oxidation treatment, a steam-containing gasor a flue gas may be used. The amount of the gas in this case may be0.1-20 Nm³ /kg, preferably 0.5-5 Nm³ /kg based on the weight of theformed material on oxidation of the formed material, an oxygenconcentration higher than 18 vol. % causes the oxidation to proceed somuch that the reaction can be hardly controlled. Excess oxidationresults in a carbonized formed material having low strength. An oxygenconcentration lower than 1 vol. % however leads to insufficientoxidation, so that the formed material tends to swell or fuse togetherin the next carbonization step and cannot provide any product improvedin desulfurization and denitrification activities. If the temperature ofthe atmosphere for this oxidation is lower than 50° C., the oxidationdoes not proceed sufficiently so that the formed material is caused toswell or fuse together. If the temperature conversely exceeds 250° C.,the oxidation proceeds so much that the strength of the formed materialis lowered. As a consequence, neither conditions meet the object of thepresent invention.

By subjecting the formed material to oxidation treatment under the aboveconditions, the caking property of the coal blend can be adjusted and anactivated coke having high strength even after carbonization can beproduced without occurrence of swelling or fused agglomeration of theformed material.

Regarding an apparatus for conducting the oxidation treatment in theabove case, no particular limitation is imposed on its shape or typeinsofar as the above-described oxidizing conditions can be realized. Forexample, a rotary kiln, a multihearth oven, a fluidized bed kiln, afixed bed oven, a vertical oven or the like can be used.

As conditions for the carbonization of the oxidized formed material, thecarbonization can be carried out at an oxygen concentration of 8 vol. %or lower, preferably 3 vol. % or lower at a temperature of 600°-900° C.At this time, the heating efficiency is set at 10°-50° C./min,preferably 20°-40° C./min. A low heating efficiency results only in acarbonized product of low strength, eventually leading to an activatedcoke of insufficient strength. A high heating efficiency, on the otherhand, lead to insufficient desulfurization and nitration performance. Ifthe oxygen concentration exceeds 8 vol. %, combustion proceeds so muchthat the strength is lowered. Upon conducting the carbonizationtreatment, a steam-containing gas or a flue gas can also be used. Theoxygen concentration may be 0 vol. % if possible.

The carbonized product so obtained is next subjected to oxidationtreatment again for 40-200 minutes under conditions of an oxygenconcentration of 3-18 vol. %, preferably 12-16 vol. % and a temperatureof 200°-600° C., preferably 350°-500° C. The amount of the gas suppliedhere may be 0.1-20 Nm³ /kg based on the weight of the carbonizedproduct. Upon conducting the oxidation treatment in this case, asteam-containing gas or a flue gas can also be used. In this secondoxidation treatment, it is also difficult to control the reaction if theoxygen concentration exceeds 18 vol. %. It is however difficult to allowthe reaction to proceed when the oxygen concentration is lower than 3vol. %. By conducting this second oxidation treatment, the carbonizedproduct is provided, as an activated coke for desulfurization anddenitrification, with enhanced surface activities while retaining highstrength, whereby activated coke excellent in both desulfurizing abilityand denitrifying ability can be obtained even if its specific surfacearea is small.

The denitrification efficiency of the activated coke obtained asdescribed above is gradually improved in its repeated use. If it isdesired to produce an activated coke having a high denitrificationefficiency from the beginning, this objective can be attained bytreating an activated coke, which has been obtained as described above,further with concentrated sulfuric acid. In this case, the concentrationof the concentrated sulfuric acid is about 50 to 100 wt. % or so and thetime of the treatment is about 1-50 minutes or so. Regarding the mannerof the treatment, the objective can be achieved by conducting dippingtreatment at room temperature. If the dipping time is shorter than 1minute, the denitrification efficiency is not substantially differentfrom that available when the dipping is not conducted. A dipping time inexcess of 50 minutes, on the other hand, results in an activated cokewith reduced strength and is hence not preferred.

As has been described above, the present invention, compared with theconventional processes, has made it possible to very easily conduct theadjustment of caking property by the oxidation of the formed coalmixture, to conduct the oxidation and carbonization steps at lowertreatment temperatures and further to increase the heating efficiency inthe carbonization step. It is therefore possible to obtain an activatedcoke having high desulfurizing and denitrifying activities withoutcausing a reduction in strength. Further, loads on treatment facilitiescan be reduced so that the treatment facilities can be constructed insmaller dimensions. These are advantages which the present invention canbring about.

In addition, it is unnecessary, different from the conventional art, toconvert a coal as a raw material into a semi-coke in advance. Theactivated coke obtained in accordance with the present invention showshigh denitrification performance even if its specific surface area issmall. This seems to be attributable to the formation of surfacefunctional groups on the surface of the activated coke by the oxidationtreatment.

EXAMPLES

The present invention will hereinafter be described specifically byexamples. It is however to be noted that these examples illustrate thebest results and the technical scope of the present invention is hencenot limited to the examples.

In the following examples, individual properties were measured by thefollowing methods:

Adsorbed SO₂ amount

An activated coke (10 cc), whose particle size had been adjusted to0.5-2.38 mm, was charged in a glass tube of 30 mm in inner diameter,through which a test gas having the following gas composition: SO₂ :20,000 ppm, O₂ : 5%, H₂ O: 10%, and N₂ : balance was caused to flow at atemperature of 100° C. for 3 hours so that SO₂ was adsorbed. Desorptionwas then conducted at 400° C. for 1 hour in an N₂ atmosphere todetermine the amount of SO₂ desorbed, which was then recorded as theadsorbed SO₂ amount.

Desulfurization efficiency

In a tubular testing apparatus whose inner diameter was 50 mm, 300 cc ofan activated coke were filled, through which a test gas containing 1,000ppm of SO₂, 5% of O₂ and 10% of H₂ O and balanced with N₂ was caused toflow at a temperature of 130° C. and a space velocity of 400 hr³¹ 1. TheSO₂ concentration in the outlet gas was measured to determined thedesulfurization efficiency.

Denitrification efficiency

In a tubular testing apparatus whose inner diameter was 50 mm, 300 cc ofan activated coke were filled, through which a test gas containing 200ppm of NO, 5% of O₂, 10% of H₂ O and 200 ppm of NH₃ and balanced with N₂was caused to flow at a temperature of 130° C. and a space velocity of400 hr⁻¹. The NO concentration in the outlet gas was measured todetermined the denitrification efficiency.

Strength of activated coke

A Roga testing apparatus specified under JIS M 8801 was used. Anactivated coke (50 cc) of 6 mm and greater in size was placed in arotary drum. After the rotary drum was driven 1,000 revolutions at arate of 50 rpm, the contents were screened using a 6-mm sieve. Thepercentage of the plus sieve residue was determined and recorded as theRoga strength.

Caking property of coal The caking property of each coal was determinedaccording to the Roga testing method specified under JIS M 8801.

Example 1

Sixty-nine parts by weight of a soft coking coal (Roga index: 47) havinga volatile content of 34% and 17 parts by weight of a hard coking coal(Roga index: 76) having a volatile content of 20% were blended. Afterthe coal blend was crushed to 0.5 mm or smaller, 14 parts by weight of acoal pitch were added. The resultant mixture was mixed and kneaded in adouble arm kneader. The mass so obtained was formed by a briquettingmachine into pieces of an almond shell shape of 17.5×13.5×9 mm indimensions, whereby a formed material was obtained. After the formedmaterial so obtained was oxidized at 170° C. and an O₂ concentration of12% for 60 minutes in a rotary kiln, the thus-oxidized coal mixture washeated at a heating efficiency of 33° C./min and was maintained forcarbonization at 850° C. for 15 minutes, so that a carbonized coalmixture was obtained. The resultant carbonized coal mixture was nextoxidized at an O₂ concentration of 15% and 470° C. for 60 minutes,whereby an activated coke whose specific surface area and Roga strengthwere 111 m² /g and 96%, respectively, was obtained.

Further, the adsorbed SO₂ amount, desulfurization. efficiency anddenitrification efficiency by this activated coke were also determinedaccording to the above-described methods. As a result, the adsorbed SO₂amount, desulfurization efficiency and denitrification efficiency werefound to be 40 mg/g, 63% and 55%, respectively.

Example 2

The procedures of Example 1 were repeated likewise except that the timeof the oxidation treatment of the carbonized coal mixture was changed to2 hours. An activated coke whose specific surface area and Roga strengthwere 185 m² /g and 95%, respectively, was obtained.

The adsorbed SO₂ amount, desulfurization efficiency and denitrificationefficiency by this activated coke were determined according to theabove-described methods. As a result, the adsorbed SO₂ amount,desulfurization efficiency and denitrification efficiency were found tobe 50 mg/g, 66% and 67%, respectively.

Comparative Example 1

A soft coking coal (Roga index: 47) having a volatile content of 34%,which had been crushed to 0.5 mm or smaller, was heat-treated at 450° C.for 10 minutes, whereby a semi-coke was obtained. Twelve parts by weightof a coal pitch were added to 76 parts by weight of the semi-coke and 12parts by weight of a hard coking coal (Roga index: 76) having a volatilecontent of 20%, said hard caking coal having been crushed to 0.5 mm orsmaller, followed by mixing and kneading in a double arm kneader. Themass so obtained was formed by a briquetting machine into pieces of analmond shell shape of 17.5×13.5×9 mm in dimensions, whereby a formedcoal mixture was obtained. The formed coal mixture so obtained washeated in an atmosphere containing 0% of O₂ at a heating efficiency of8° C./min in a rotary kiln and was then maintained for carbonization at850° C. for 30 minutes, so that a carbonized coal mixture was obtained.The resultant carbonized coal mixture was next activated by steam at900° C. for 15 minutes, whereby an activated coke whose specific surfacearea and Roga strength were 150 m² /g and 95%, respectively, wasobtained. The adsorbed SO₂ amount, desulfurization efficiency anddenitrification efficiency of the thus-obtained activated coke were 50mg/g, 50% and 35%, respectively. As has been demonstrated above, it isunderstood that an activated coke available from the conventionalprocess has low denitrifying activity although its strength is high.

Comparative Example 2

Eighty-four parts by weight of a soft coking coal (Roga index: 47)having a volatile content of 34% and 4 parts by weight of a hard cokingcoal (Roga index: 76) having a volatile content of 20% were blended.After the coal blend was crushed to 0.5 mm or smaller, 12 parts byweight of a coal pitch were added. The resultant mixture was mixed andkneaded in a double arm kneader. The mass so obtained was formed by abriquetting machine into pieces of an almond shell shape of 17.5×13.5×9mm in dimensions, whereby a formed coal mixture was obtained. After theformed coal mixture so obtained was oxidized at 170° C. and an O₂concentration of 12% for 60 minutes in a rotary kiln, the thus-oxidizedcoal mixture was heated at a heating efficiency of 33° C./min and wasmaintained for carbonization at 850° C. for 15 minutes, so that acarbonized coal mixture was obtained. The resultant carbonized coalmixture was next oxidized at an O₂ concentration of 15% and 470° C. for60 minutes, whereby an activated coke whose specific surface area andRoga strength were 126 m² /g and 88%, respectively, was obtained.

It is understood from the above results that even a blend of cakingcoals cannot provide an activated coke of high strength when theproportion of the caking coal of higher caking property does not fallwithin the range specified in the present invention. Further, theadsorbed SO₂ amount, desulfurization efficiency and denitrificationefficiency of the thus-obtained activated coke were 52 mg/g, 71% and58%, respectively.

Comparative Example 3

Sixty-nine parts by weight of a soft coking coal (Roga index: 47) havinga volatile content of 34% and 17 parts by weight of a hard coking coal(Roga index: 76) having a volatile content of 20% were blended. Afterthe coal blend was crushed to 0.5 mm or smaller, 14 parts by weight of acoal pitch were added. The resultant mixture was mixed and kneaded in adouble arm kneader. The mass so obtained was formed by a briquettingmachine into pieces of an almond shell shape of 17.5×13.5×9 mm indimensions, whereby a formed coal mixture was obtained. After the formedcoal mixture so obtained was oxidized at 170° C. and an O₂ concentrationof 5% for 30 minutes in a rotary kiln, the thus-oxidized coal mixturewas heated at a heating efficiency of 33° C./min and was maintained forcarbonization at 850° C. for 15 minutes, so that a carbonized coalmixture was obtained. The resultant carbonized coal mixture was nextoxidized at an O₂ concentration of 15% and 470° C. for 60 minutes,whereby an activated coke whose specific surface area and Roga strengthwere 70 m² /g and 96%, respectively, was obtained. Further, the adsorbedSO₂ amount, desulfurization efficiency and denitrification efficiency ofthe thus-obtained activated coke were 28 mg/g, 35% and 38%,respectively.

Example 3

The activated coke obtained in Example 1 was dipped at room temperaturefor 30 minutes in a 98% concentrated sulfuric acid solution and was thendried, whereby an activated coke improved in denitrification efficiencywas obtained. An activated coke whose specific surface area and Rogastrength as properties thereof were 158 m² /g and 96%, respectively, wasobtained. Further, the adsorbed SO₂ amount, desulfurization efficiencyand denitrification efficiency of the thus-obtained activated coke were52 mg/g, 65% and 60%, respectively.

Comparative Example 4

After the activated coke obtained in Example 1 was dipped for 1 hour ina concentrated sulfuric acid solution, the thus-dipped activated cokewas heat-treated at 400° C. for 1 hour in a nitrogen atmosphere, wherebyan activated coke whose specific surface area and Roga strength asproperties thereof were 168 m² /g and 93%, respectively, was obtained.Further, the adsorbed SO₂ amount, desulfurization efficiency anddenitrification efficiency of the thus-obtained activated coke were 55mg/g, 69% and 62%, respectively.

Comparative Example 5

The procedures of Example 1 were repeated likewise except that theoxidization treatment of the carbonized coal mixture was not conducted.An activated coke whose specific surface area and Roga strength were 36m² /g and 97%, respectively, was obtained.

The adsorbed SO₂ amount, desulfurization efficiency and denitrificationefficiency by this activated coke were found to be 9 mg/g, 21% and 22%,respectively. It is understood that an activated coke available from aprocess, in which oxidization treatment of a carbonized coal mixture isnot conducted, is low in desulfurization and denitrification activitiesalthough it may have high strength.

Comparative Example 6

The procedures of Example 1 were repeated likewise except that the timeof the oxidization treatment was changed to 30 minutes. An activatedcoke whose specific surface area and Roga strength were 81 m² /g and96%, respectively, was obtained.

The adsorbed SO₂ amount, desulfurization efficiency and denitrificationefficiency by this activated coke were found to be 27 mg/g, 44% and 41%,respectively. It is understood that, where the oxidation treatment of acarbonized coal mixture is insufficient, the resulting activated cokemay have high strength but is low in desulfurization and denitrificationactivities although its desulfurization and denitrification activitiesare not so low as in Comparative Example 5.

Comparative Example 7

The procedures of Example 1 were repeated likewise except that theheating efficiency in the carbonization procedure was changed to 5°C./min. An activated coke whose specific surface area and Roga strengthwere 120 m² /g and 92%, respectively, was obtained.

It is understood from the above results that no high-strength activatedcoke can be obtained when the heating efficiency in the carbonizationprocedure is slow. Further, the adsorbed SO₂ amount, desulfurizationefficiency and denitrification efficiency of the thus-obtained activatedcoke were 49 mg/g, 69% and 59%, respectively.

Comparative Example 8

The procedures of Example 1 were repeated likewise except that theheating efficiency in the carbonization procedure was changed to 100°C./min. An activated coke whose specific surface area and Roga strengthwere 75 m² /g and 96%, respectively, was obtained.

The adsorbed SO₂ amount, desulfurization efficiency and denitrificationefficiency of the thus-obtained activated coke were 21 mg/g, 32% and30%, respectively. It is hence understood that, where the heatingefficiency is high in the carbonization procedure, the resultingactivated coke is low in desulfurization and denitrification activitiesalthough it may have high strength.

CAPABILITY OF EXPLOITATION IN INDUSTRY

According to the present invention, upon production of an activatedcoke, at last two coals of different caking properties, including atleast one caking coal, are blended to obtain a formed coal mixture, andthe formed coal mixture is then subjected to oxidation treatment. Thishas obviated the need for conversion of coals as raw materials into asemi-coke in advance in the conventional production process for anactivated coke. Further, the adjustment of caking property can beconducted very easily and the oxidation and carbonization steps can bepracticed at low treatment temperatures. In addition, the heatingefficiency of the carbonization step can be increased. It is thereforepossible to obtain an activated coke having high desulfurization anddenitrification activities without inducing a reduction in strength.Moreover, the present invention can also bring about the advantage thatloads on treatment facilities can be reduced and the treatmentfacilities can thus be constructed in smaller dimensions.

We claim:
 1. A process for production of a high-strength activated cokefor desulfurization and denitrification from coal as a principal rawmaterial, which comprises the steps of:blending at least one caking coaland at least one non-caking coal or at least two caking coals ofdifferent caking properties to provides a coal blend 10-50 wt. % of saidcaking coal or caking coal of greater caking property and a diameter of5-20 mm; adding a binder to said coal blend to provide a mixture;kneading said mixture to provide a kneaded mixture; forming theresultant mixture in a briquetting machine, pelletizer, or extruder toprovide a formed material having a diameter of 5-20 mm; oxidizing saidformed material in an atmosphere having an oxygen concentration of 1-18vol. % and a temperature of 50°-250° C. for a period of 10-180 minutes,with a supply gas being 0.1-20 Nm³ /kg based on said formed material toprovide a oxidized mixture; carbonizing said oxidized mixture at anoxygen concentration not higher than 8 vol. % and a heating efficiencyof 20°-40° C./min to a final temperature 600°-900° C. to provide acarbonized mixture; and oxidizing said carbonized mixture in anatmosphere having an oxygen concentration of 12-16 vol. % and atemperature of 350°-500° C. for a period of 40-200 minutes, with asupply gas being 1-20 Nm³ /kg based on said carbonized mixture.
 2. Aprocess for production of a high-strength activated coke fordesulfurization and denitrification, which comprises:forming a mixtureof plural coals of different caking properties and a binder, saidmixture containing a coal of higher caking property in an amount of10-50 wt. % and having a diameter of no more than 0.5 mm; kneading saidmixture to provide a kneaded material; forming said kneaded material ina briquetting machine, pelletizer, or extruder to provide a formedmixture having a diameter of 5-20 mm; subjecting the thus-formed mixtureto oxidization treatment in an atmosphere having an oxygen concentrationof 1-18 vol. % and a temperature of 50°-250° C. for a period of 1-180minutes, with a supply gas being 0.1-20 Nm³ /kg based on said formedmixture to provide a treated mixture; subjecting the thus-treatedmixture to carbonization treatment under conditions of an oxygenconcentration not higher than 8 wt. %, a heating efficiency of 20°-40°C./min and a final temperature 600°-900° C. provide a carbonizedmixture; and then subjecting again the thus-carbonized mixture tooxidation treatment in an atmosphere having an oxygen concentration of12-16 vol. % and a temperature of 350°-500° C. for period of 40-200minutes, with a supply gas being 0.1-20 Nm³ /kg based on said carbonizedmixture.
 3. A process for production of a high-strength activated cokefor desulfurization and denitrification, which comprises:forming amixture of plural coals of different caking properties and a binder,said mixture containing a coal of higher caking property in an amount of10-50 wt. % and having a diameter of no more than 0.5 mm; kneading saidmixture in a briquetting machine, pelletizer, or extruder to provide aformed mixture having a diameter of 5-20 mm; subjecting the thus-formedmixture to oxidization treatment in an atmosphere having an oxygenconcentration of 1-18 vol. % and a temperature of 50°-250° C. for aperiod of 10-180 minutes, with a supply gas being 0.1-20 Nm³ /kg basedon said formed mixture; subjecting the thus-treated mixture tocarbonization treatment under conditions of an oxygen concentration nothigher than 8 vol. %, a heating efficiency of 20°-40° C./min and a finaltemperature 600°-900° C.; subjecting again the thus-carbonized mixtureto oxidation treatment at an oxygen concentration of 12-16 vol. % and atemperature of 350°-500° C. for a period of 40-200 minutes, with asupply gas being 0.1-20 Nm³ /kg based on said carbonized mixture;subjecting the thus-reoxidized mixture to dipping treatment for 1-50minutes in concentrated sulfuric acid; and then drying the thus-dippedmaterial.